AN EVAPORATOR ASSEMBLY

Abstract

An evaporator assembly comprises at least one plate evaporator, each plate evaporator comprising first and second sheets that are joined together and that define an internal conduit between the sheets. The internal conduit is aligned parallel to the sheets and is configured to carry refrigerant through the plate evaporator, each plate evaporator further comprising a first electrically insulative layer applied on the first sheet, an electrically resistive layer applied on the first electrically insulative layer, and a second electrically insulative layer applied on the electrically resistive layer. The electrically resistive layer is an elongated track that follows a meandering path traversing along the first sheet.

Claims

1. An evaporator assembly comprising at least one plate evaporator, each plate evaporator comprising first and second sheets that are joined together and that define an internal conduit between the sheets, the internal conduit aligned parallel to the sheets and configured to carry refrigerant through the plate evaporator, each plate evaporator further comprising a first electrically insulative layer applied on the first sheet, an electrically resistive layer applied on the first electrically insulative layer, and a second electrically insulative layer applied on the electrically resistive layer, wherein the electrically resistive layer is an elongated track that follows a meandering path traversing along the first sheet.

2. The evaporator assembly of claim 1, wherein the first electrically insulative layer is also an elongated track that follows the meandering path, between the first sheet and the electrically insulative layer.

3. The evaporator assembly of claim 1, wherein the second electrically insulative layer extends over and encapsulates both the first and the second sheets.

4. The evaporator assembly of claim 1, wherein the internal conduit follows at least a portion of the meandering path.

5. The evaporator assembly of claim 1, wherein the first electrically insulative layer adheres to the first sheet, and wherein the electrically resistive layer adheres to the first electrically insulative layer.

6. The evaporator assembly of claim 5, wherein the first electrically insulative layer is a paint layer that is painted on the first sheet.

7. The evaporator assembly of claim 5, wherein the electrically resistive layer is a paint layer that is painted on the first electrically insulative layer.

8. The evaporator assembly of claim 7, wherein the paint of the electrically resistive layer comprises a nickel-chromium powder.

9. The evaporator assembly of claim 1, wherein the second electrically insulative layer forms an exterior surface of the plate evaporator.

10. The evaporator assembly of claim 1, wherein the second electrically insulative layer is applied directly to the second sheet without any first insulative layer or electrically resistive layer between the second electrically insulative layer and the second sheet.

11. The evaporator assembly of claim 1, wherein the first and second sheets are metal sheets.

12. The evaporator assembly of claim 1, comprising a heater control unit that is electrically connected to opposing ends of the elongated track of the electrically resistive layer, and configured to drive an electric current along the elongated track of the electrically resistive layer to heat the plate evaporator in a defrost mode.

13. The evaporator assembly of claim 12, wherein the heater control unit is configured to receive a signal indicating when the flow of refrigerant through the plate evaporator has ceased, and to only enter the defrost mode of the plate evaporator when the signal indicates the flow of refrigerant through the plate evaporator has ceased.

14. The evaporator assembly of claim 1, comprising a plurality of the plate evaporators arranged parallel to one another, and further comprising an inlet manifold for connecting to a compressor, an outlet manifold for connecting to a condenser, and pipes connecting the internal conduits of the plate evaporators to the inlet and outlet manifolds.

15. The evaporator assembly of claim 14, comprising a heater control unit that is electrically connected to opposing ends of the elongated track of the electrically resistive layer of each plate evaporator, and configured to drive an electric current along the elongated track of the electrically resistive layer to heat the plate evaporator in a defrost mode, wherein the heater control unit is configured to drive an electric current through the elongated tracks of the plate evaporators in sequence such that the plate evaporators are not all in the defrost mode at a same time as one another.

16. The evaporator assembly of claim 15, wherein the heater control unit is configured to receive a signal indicating when the flow of refrigerant through the plate evaporators has ceased, and to only enter the defrost mode of each plate evaporator when the signal indicates the flow of refrigerant through the plate evaporator has ceased, wherein the heater control unit is configured to enter the defrost mode of at least one of the plate evaporators every time that the signal is received indicating the flow of refrigerant has ceased.

17. The evaporator assembly of claim 15, wherein the heater control unit is configured to enter the defrost mode of only one plate evaporator at a time.

18. The evaporator assembly of claim 16, wherein the plate evaporators are arranged with the first sheet and the second sheet of immediately adjacent plate evaporators facing towards one another.

19. An evaporator system comprising at least one plate evaporator, each plate evaporator comprising first and second sheets that are joined together and that define an internal conduit between the sheets, the internal conduit aligned parallel to the sheets and configured to carry refrigerant through the plate evaporator, each plate evaporator further comprising a first electrically insulative layer applied on the first sheet, an electrically resistive layer applied on the first electrically insulative layer, and a second electrically insulative layer applied on the electrically resistive layer, wherein the electrically resistive layer is an elongated track that follows a meandering path traversing along the first sheet.

20. The system of claim 19 including a temperature sensing element configured to sense temperature within a refrigeration space to be refrigerated by the at least one plate evaporator, and a controller configured to control the flow of refrigerant through the at least one plate evaporator based on the temperature sensing element, wherein the temperature sensing element comprises a food simulant material and a temperature probe embedded within the food simulant material, wherein the food simulant material is preferably a solid wax in which are distributed a plurality of gas-filled polymeric particles.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0036] Embodiments of the invention will now be described by way of non-limiting example only and with reference to the accompanying drawings, in which:

[0037] FIG. 1 shows a schematic diagram of a plate evaporator assembly comprising a plate evaporator in accordance with an embodiment of the invention;

[0038] FIG. 2 shows a schematic cross-sectional diagram of the plate evaporator of FIG. 1;

[0039] FIG. 3 shows a schematic diagram of a plate evaporator assembly comprising a plurality of the plate evaporators of FIG. 1; and

[0040] FIG. 4 shows a schematic diagram of a refrigeration system comprising the plate evaporator assembly of FIG. 3.

[0041] The figures are not to scale, and same or similar reference signs denote same or similar features.

[0042] A first embodiment of the invention will now be described with reference to FIGS. 1 and 2, and FIG. 1 shows a plate evaporator assembly comprising a plate evaporator 10. The plate evaporator 10 comprises a first sheet 11 which may be aluminium, and second sheet 12 which may also be aluminium. The first and second sheets may be substantially planar and fixed on top of one another in a stacked arrangement.

[0043] The first and second sheets 11 and 12 have shapes that define an internal conduit 16 between them when the first and second sheets are joined together. The internal conduit 16 may meander over the area between the first and second sheets, parallel to the first and second sheets, traversing over the majority of the area between the first and second sheets. The internal conduit 16 may be connected to an inlet 15 at one end of the internal conduit 16 for receiving refrigerant from a compressor, and connected to an outlet 17 at an opposite end of the internal conduit 16 for out letting the refrigerant to a condenser when the evaporator is in use.

[0044] The first sheet 11 may have a first electrically insulative layer 20 of a material that is painted onto the outer surface of the first sheet and that follows a meandering path over the area of the first sheet. The first electrically insulative layer 20 may be a polymer based paint, which may have been applied to the outer surface of the first sheet by a spray process. The first electrically insulative layer 20 is preferably in the form of an elongated track running parallel to and conforming to the surface of the first sheet, as shown.

[0045] The first electrically insulative layer 20 may have an electrically resistive layer 21 painted upon it, the electrically resistive layer 21 being an elongated track that follows the same meandering path as the first electrically insulative layer 20. The electrically resistive layer 21 may be a layer of paint comprising a nickel-chromium powder that allows flow of electric current through the paint, however other types of electrically resistive paint could alternatively be used. The width of the elongated track of the electrically resistive layer 21 may be less than the width of the elongated track of the first electrically insulative layer 20, such that the first electrically insulative layer 20 extends beyond the electrically resistive layer 21 at both side edges of the electrically resistive layer 21, as shown. The elongated track of the electrically resistive layer 21 may traverse over (across) approximately 75% of the whole area of the first sheet 11, as shown.

[0046] The internal conduit 16 may follow a least a portion of the meandering path taken by the electrically resistive layer 21, for example FIG. 1 identifies a portion P1 where the internal conduit 16 follows the meandering path of the electrically resistive layer 21 vertically, and another portion P2 where the internal conduit 16 follows the meandering path of the electrically resistive layer 21 horizontally.

[0047] The elongated track of the electrically resistive layer 21 has a positive electric terminal pad 22 at one end of the elongated track and a negative electric terminal pad 24 at an opposite end of the elongated track. The positive and negative electric terminal pads 22 and 24 are connected to positive and negative wires 23 and 25, respectively, for connection to an electrical power source. When the electrical power source drives electric current through the elongated track of the electrically resistive layer 21, ohmic heating raises the temperature of the electrically resistive layer 21, and the heat is conducted through the first electrically insulative layer 20 to the first sheet 11 and subsequently to the second sheet 12. The first electrically insulative layer 20 prevents shorting of the electrical current to the first sheet 11.

[0048] The plate evaporator also has a second electrically insulative layer 28 which may be applied to and over the electrically resistive layer 21, the first electrically insulative layer 20 and the first and second sheets 11 and 12. This is best seen in FIG. 2 which shows a cross-sectional view of the plate evaporator 10 taken along line XS1 marked on FIG. 1. As shown in FIG. 2, the first and second sheets 11 and 12 may each have complimentary ridges 16a and 16b which coincide with one another to define the internal conduit 16 between the first and second sheets. Alternatively, the ridges could only be formed on one of the two sheets if desired.

[0049] The rightmost part of the internal conduit shown in FIG. 2 is part of the plate evaporator that may have the first electrically insulative layer 20 painted on the outside surface of the first sheet 11, and the electrically resistive layer 21 painted on the first electrically insulative layer 20, as shown. The second electrically insulative layer 28 may be formed as an enamel coating over the first and second sheets 11 and 12, the first electrically insulative layer 20, and the electrically resistive layer 21, to provide a sanitary exterior surface of the plate evaporator that protects the interior of the plate evaporator from the external environment. The second electrically insulative layer 28 may encapsulate the first and second sheets 11 and 12, surrounding them on all sides.

[0050] The second plate 12 may be devoid of any electrically resistive layer, and the second electrically insulative layer 28 may directly contact the second plate 12 over the whole outer surface of the second plate 12.

[0051] It would alternatively be possible to apply the first electrically insulative layer 20 over the whole of the surface of the first sheet rather than in the shape of an elongated track. For example, the first electrically insulative layer could be applied as a coating over the whole of the plate evaporator, and the second electrically insulative layer could be formed as an elongated track over the meandering path of the electrically resistive layer, with the exterior surface of the plate evaporator then being formed by the first electrically insulative layer, except for the areas where the elongated track of the second electrically insulative layer was present.

[0052] In use, a compressor pumps refrigerant into the inlet 15 and through the internal conduit 16, absorbing heat from the first and second sheets 11 and 12 as the refrigerant evaporates within the internal conduit. This rapidly lowers the temperature of the first and second sheets, and also the exterior of the plate evaporator. There is minimal thermal resistance between the exterior of the plate evaporator and the refrigerant, since the first insulative layer 20 and the resistive layer 21 are only present over a small area of the overall exterior surface area of the plate evaporator, and heat only needs to conduct through the second electrically insulative layer 28 and the sheets 11 and 12 to reach the refrigerant over the majority of the exterior surface area of the plate evaporator.

[0053] After a period of operation ice may begin to form on the exterior surface of the plate evaporator, and the electric current may be passed through the electrically resistive layer 21 in a defrost mode that defrosts the ice and prevents it from building up significantly over time. The electric current provides gentle heating of the electrically resistive layer 21, the heat conducting though the plate evaporator and melting any ice present on the exterior surfaces of the plate evaporator. The temperature of the exterior surfaces of the plate evaporator may for example be raised to up to 5 degrees centigrade, sufficient to defrost any ice without significantly raising the temperature inside the space that is being refrigerated.

[0054] The schematic diagram of FIG. 3 shows another plate evaporator assembly 6 in which five of the plate evaporators 10 of FIG. 1 may be assembled together to form a multi-plate evaporator assembly. Each plate evaporator may have four threaded holes 36 around the periphery of the plate evaporator, which receive four threaded rods 32, 33, 34 and 35 to secure the plate evaporators 10 together. In an alternate embodiment the holes 36 may not be threaded and nuts may be screwed onto the threaded rods 32, 33, 34 and 35 to secure the plate evaporators 10 in the desired positions.

[0055] The inlets 15 of the plate evaporators 10 may be connected to a common inlet manifold 30, and the outlets 17 of the plate evaporators 10 may be connected to a common outlet manifold 31. The inlet manifold 30 may be for connecting to a compressor and the outlet manifold 31 may be for connecting to a condenser.

[0056] The positive wires 23 of the evaporator plates 10 may be bundled together into a cable 23a, and the negative wires 25 of the evaporator plates 10 may be bundled together into a cable 25a. The cables 23a and 25a may be connected to a heater control unit, to control the heating of each of the plate evaporators 10. Clearly there are a myriad of different ways in which the positive and negative wires could be bundled together into cables for connecting to the heater control unit.

[0057] In this embodiment there are five of the evaporator plates 10, however alternative embodiments may have alternate numbers of evaporator plates.

[0058] The schematic diagram of FIG. 4 shows a refrigeration system comprising the plate evaporator assembly 6 of FIG. 3. The plate evaporator assembly 6 is shown being used to refrigerate a refrigerated space 40. The refrigerated space 40 may for example be a commercial chiller, freezer or cold room, from the very small to the very large.

[0059] The bundles of cables 23a and 25a of the plate evaporator assembly 6 may be connected to a heater control unit 50, which is configured to control when the plate evaporators are heated. The heater control unit may enter a defrost mode of one or more of the plate evaporators, in which the heater control unit applies a voltage across the wires 23 and 25 connected to the plate evaporator, to drive an electric current through the electrically resistive layer of the plate evaporator. The heater control unit may for example apply a voltage of 24V and current of 3 A to each pair to wires 23 and 25 corresponding to one of the plate evaporators. The heater control unit may apply the voltage and current for long enough to raise the temperature of the plate evaporator to approximately 5 degrees centigrade, which may take a minute or two. Preferably, the heater control unit only heats one plate evaporator at a time, and so the heater control unit does not have to supply any more current that that which is drawn by a single plate evaporator.

[0060] The inlet manifold 30 may be connected to an outlet of a compressor 55, and the outlet manifold 31 may be connected to an inlet of a condenser 56. An outlet of the condenser may be connected to an inlet of the compressor, forming a closed path around which refrigerant can be pumped by the compressor, to refrigerate the space 40.

[0061] The refrigeration system may also comprise a temperature sensing element 45 that is configured to sense the temperature within the refrigeration space 40. The temperature sensing element comprises a food simulant material 46 and a temperature probe 47 embedded within the food simulant material. The food simulant material may be a solid wax in which are distributed a plurality of gas-filled polymeric particles, for example polystyrene balls. The temperature sensing element 45 may also comprise a cable 48 for outputting temperature measurements, the temperature measurements being similar to the temperatures of any foods that are stored within the refrigerated space.

[0062] The refrigeration system may also comprise a controller 57, which is connected to the cable 48 of the temperature sensing element 45. The controller 57 may also be connected to the compressor 55, and to the heater control unit 50. The controller sends a signals to the compressor 55 instructing the compressor to turn on and off, and also sends signals 58 to the heater control unit 30, informing the heater control unit 30 of whether the compressor is turned on or off.

[0063] The controller 57 may control the flow of refrigerant through the at least one plate evaporator by turning the compressor on and off, based on the temperature reported by the temperature sensing element 45, to regulate the temperature of any food that may be stored in the refrigerated space 40.

[0064] In use, when the temperature reported by the temperature sensing element 45 rises too high, the controller 57 instructs the compressor 55 to start pumping, and informs the heater control unit 50 that flow of refrigerant has begun, causing the heater control unit 50 to exit any defrost modes that were active. Once the temperature reported by the temperature sensing element 45 has lowered sufficiently, the controller 57 instructs the compressor 55 to stop pumping, and informs the heater control unit 50 that flow of refrigerant has ceased. The heater control unit 50 then enters a defrost mode of one of the plate evaporators, passing current through the electrically resistive layer of that plate evaporator, and may continue for a minute or so, before ceasing and entering the defrost mode of the next plate evaporator. The heater control unit 50 steps through the defrost modes of the plate evaporators in sequence, until all the of the plate evaporators have been defrosted, or until the controller 57 signals that the compressor is going to start pumping again. It would also be possible for the heater control unit to repeatedly cycle though all of the plate evaporators whilst the flow of refrigerant has ceased, spending a short time (for example 5 or 10 seconds) in the defrost mode of each plate evaporator before moving on to the next plate evaporator. Then, all the plate evaporators are defrosted at a similar time and rate to one another.

[0065] Many other variations of the described embodiments falling within the scope of the invention will be apparent to those skilled in the art.